[patch]block cfq: select new workload if priority changed

[Shaohua Li <shaohua.li@intel.com>]

If priority is changed, continue checking workload_expires and service tree
count of previous workload is meaningless. We should always choose the workload
with lowest key of new priority in such case.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>
---
 block/cfq-iosched.c |    5 +++++
 1 file changed, 5 insertions(+)

Index: linux/block/cfq-iosched.c
===================================================================
--- linux.orig/block/cfq-iosched.c	2010-12-08 19:39:01.000000000 +0800
+++ linux/block/cfq-iosched.c	2010-12-09 10:27:24.000000000 +0800
@@ -2116,6 +2116,7 @@ static void choose_service_tree(struct c
 	unsigned count;
 	struct cfq_rb_root *st;
 	unsigned group_slice;
+	enum wl_prio_t original_prio = cfqd->serving_prio;
 
 	if (!cfqg) {
 		cfqd->serving_prio = IDLE_WORKLOAD;
@@ -2134,6 +2135,9 @@ static void choose_service_tree(struct c
 		return;
 	}
 
+	if (original_prio != cfqd->serving_prio)
+		goto new_workload;
+
 	/*
 	 * For RT and BE, we have to choose also the type
 	 * (SYNC, SYNC_NOIDLE, ASYNC), and to compute a workload
@@ -2148,6 +2152,7 @@ static void choose_service_tree(struct c
 	if (count && !time_after(jiffies, cfqd->workload_expires))
 		return;
 
+new_workload:
 	/* otherwise select new workload type */
 	cfqd->serving_type =
 		cfq_choose_wl(cfqd, cfqg, cfqd->serving_prio);